Abstract: https://reurl.cc/NNZgGe
Phonons are the quasiparticles of lattice vibrations and represent the primary heat carriers in bulk dielectric materials. The thermal conductivity of dielectric low-dimensional solids is thus typically driven by acoustic phonons and generally reduces with thickness due to surface scattering events [1]. Yet, heat transport might reversely be enhanced via hybrid excitations, i.e. surface phonon-polaritons or plasmon-polaritons.
Over the two past decades, substantial research efforts have been devoted to the study of those modes, especially due to their ability to transfer an exalted heat flux through submicron gaps [2]. Surface polaritons are essentially evanescent waves in the out-of-plane direction but propagate along the surface of polar dielectrics.
More recently, it has been theoretically proposed that polaritons could also carry an in-plane heat flux, especially in thin films, where those modes cover a large spectrum and have extremely long propagation lengths. Theoretical models predicted that such propagation lengths enable a larger heat conduction via polaritons than via phonons [3,4].
In this seminar, the existence and the properties of those film-polaritons will be demonstrated [5] then the experimental measurement of the corresponding heat flux will be presented [6,7,8]. Our recent theoretical investigations confirm the match between measurements and predictions within 5% of inaccuracy [9].
Further measurements investigating thermal radiation of films beyond the reactive near-field will be also introduced. In particular, a debated Super Planckian heat flux was observed [10].
Acknowledgements: This work is supported by CREST JST, Grant JPMJCR19I1.